New SIZE_VERBOSE option for firmware and example targets.

If selected, it will print something like

AVR Memory Usage
----------------
Device: atmega32u4

Program:   19780 bytes (60.4% Full)
(.text + .data + .bootloader)

Data:       1949 bytes (76.1% Full)
(.data + .bss + .noinit)

This helps to understand, how much memory is left for code and how much RAM is available for stack.
Update README.rst
Minor documentation fix
Merge remote-tracking branch 'plin/verbose_size' into verbose_size_integration

Conflicts:
	cmake/Platform/Arduino.cmake
Major refactoring of verbose_size feature, condensed verbose output by default, added VERBOSE_SIZE option to enable full avr-size output, added Pavel Ilin to contibutors
Merge branch 'verbose_size_integration' into develop, fixes issue #58